(1) Field of the Invention
The invention relates to the field of fluorescent lighting which is excited by light emitting diodes.
(2) Description of the Prior Art
Early artificial lighting technology has utilized a metal filament, such as tungsten contained within an enclosed glass tube upon which a vacuum is drawn. An electric current is passed across the filament and the metal begins to glow white hot due to the resistance of the tungsten to the flowing electrons in the electric current. This concept results in an extremely low energy conversion rate of electricity utilized to provide visible light because of the large heat losses and relatively short life span of the tungsten filament. Nevertheless, this incandescent light technology has been commercially successful for quite some time.
In the late 1930's, fluorescent light technology resulted in considerable energy savings over that required in incandescent systems. The typical fluorescent lamp is an electrical discharge device which utilizes a low-pressure mercury vapor arc to generate an ultra-violet energy source. This energy is absorbed by a coating of phosphorous on the inside of a glass tube and the phosphor converts the ultra-violet energy to a visible wavelength of a particular color. The process by which phosphor absorbs the ultra-violet radiation and de-excites by admitting visible radiation is commonly referred to as fluorescence. The wavelengths of the generated light are determined by the composition of the phosphor, and such composition and phosphor determination and calculation to obtain the desired wavelength and, in turn, the achieved light color, are well known to those skilled in the art and is not part of this invention, per se. For example, the phosphor may be a fluoride of lanthanum, gadolinium or yttrium activated by erbium or thulium and sensitized by either ytterbium. These phosphors have an excitation spectrum extending from approximately 9000 to 10,400 A. Oxy sulfides of lanthanum gadolinium or yttrium and activated by erbium or thulium and thereafter sensitized by ytterbium also may he utilized. The phosphor may be coated onto the transparent, preferably glass, enclosure portion of the lighting assembly in a number of ways. It may be suspended in a suitable binder and painted onto the surface or phosphor crystals may be grown on such surface for ultimate contact with the light emitting diode crystals and the crystals may be ground and polished on one face and cemented together with transparent cement, or the like.
There are many advantages and disadvantages to mercury-based fluorescent lighting. First, the advantages include better lumen efficacy than incandescent lighting and an expected average life span in excess of 10 to 20 times. Thus, fluorescent technology decreases the number of lamps utilized for a given time period and the labor associated with replacing the incandescent bulb. Conversely, the disadvantages of fluorescent lighting include less than ideal energy conversion to light (only about 23% of the total lamp wattage in a standard fluorescent lamp is actually transformed into visible light), the need for heavy and costly electrical componentry to start and regulate the arc within the lamp, and the presence of mercury and rare earth gases (usually argon, krypton, neon, or a mixture of these) at lamp disposal which are potentially environmentally damaging.
Applicant is aware of the following prior art patents which generally relate to the subject matter of the present invention:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,529,200 Potter et al 3,591,941 Jaffe 3,593,055 Geusic et al 3,659,136 Grodkiewicz 3,774,086 Vincent 4,035,686 Fleming 4,385,343 Plumly 4,473,834 Soclof 4,847,508 Kokubu 5,020,252 De Boef 5,251,392 McManigal 5,276,591 Hagerty 5,365,411 Rycroft 5,452,190 Priesemuth 5,640,792 Smith et al 5,653,523 Roberts ______________________________________
The present invention is directed to overcoming the problems associated with the prior art, as described above.